In present information storage systems utilizing flexible disk-type media, the media is typically enclosed within a cartridge or a sleeve for insertion into a disk drive. A drive spindle engages the media at a hub, and the disk is rotated about a central axis. Information is generally recorded to or read from the outside surfaces of the media by either a magnetic head in a magnetic disk drive, an optical head in an optical disk drive or a combination magnetic and optical head in a magneto-optical disk drive. Typically the outside surface of the media is covered with an active layer in which recording of information occurs.
In a magnetic disk drive the spacing between the magnetic head and the media active layer must be very small and accurately controlled in order to allow the magnetic coil and gap on the magnetic head to either change the polarity of the magnetic media during a write operation, or to sense the polarity of the media during a read operation, over a small precise location on the media. In an optical disk drive the spacing between the objective lens on the optical head and the media active layer must be accurately controlled in order to allow a laser beam to be focused onto a small precise location on the media disk.
In a magnetic disk drive for flexible magnetic media the magnetic heads are either suspended on a flexure mechanism which allows them to accurately follow the surface contour of the media or the magnetic heads are designed to make the media conform to the contour of the head, as in a Bernoulli stabilized disk drive disclosed in U.S. Pat. No. 4,414,592--Losee et al.
In an optical disk drive for flexible optical media the optical head is either provided with a focus motor which allows the focused beam to accurately follow the surface contour of the media or a feature of the cartridge, optical head or both is designed to make the media conform to the focus requirements of the optical head.
One approach for forcing optical media to conform has been the provision of gross and fine Bernoulli stabilization. Such a system is disclosed in U.S. patent application Ser. No. 167,652, filed Mar. 14, 1988 and entitled OPTICAL READ/WRITE STORAGE SYSTEM FOR FLEXIBLE MEDIA HAVING BERNOULLI STABILIZATION AT THE OPTICAL HEAD, owned by the Assignee of the present invention. In that system, a Bernoulli surface provides gross stabilization to the flexible optical media while a coupler element provides fine Bernoulli stabilization in the region immediately proximate the optical head assembly objective lens.
In a magnetic flexible media disk drive the magnetic heads are either retracted and lifted away from the outer surface of the media during insertion of the media or the edges of the magnetic heads, which could possibly engage the media during insertion, are carefully contoured to allow the media to slip over the edge of the magnetic head with minimum force. In an optical disk drive which uses a focus motor the optical heads are located far enough away from the media area during media insertion so that no contact is made with the media. In an optical disk drive which uses Bernoulli stabilization on the optical head, the heads are contoured to allow the media to slide over the edge of the optical head during insertion of the media cartridge.
In the aforementioned magnetic and optical flexible media disk drives the heads and/or stabilizing mechanisms are only used on the outer (active layer) surface of the media. In the case of the magnetic flexible media disk drives or in the case of optical flexible media disk drives which use Bernoulli stabilization on the optical head there can exist continuous or intermittent contact of the head with the active surface of the media. This can cause wear or damage to the recording layer. This problem is much more severe in the case of the optical disk drive which uses Bernoulli stabilization on the active surface because the recording density of the optical media is much higher than that of the magnetic media. A scratch on a flexible disk which is small enough to be ignored by the magnetic head in a magnetic disk drive could easily be large enough to destroy many bytes or tracks of information in an optical disk drive. Additionally, in the case of both the magnetic flexible media disk drives and the optical flexible media disk drive the present insertion techniques limit the number of heads which can be used in a flexible media drive, since the heads are constrained to the outer surface of the media only.
In certain situations, the closeness of the media to the fine stabilization surface has exhibited excessive wear. As will be appreciated, such wear will cause reflection phase shifts. If the wear is significant, i.e., a scratch, such reflection phase shifts can reach between 180.degree. and 360.degree..
These problems are magnified if one is using cartridges having multiple disks, such as that disclosed in U.S. Pat. No. 4,743,989--Bauck et al.
Consequently, a need exists to stabilize flexible media, while simultaneously locating the optical head a sufficient distance from the media to eliminate wear and further maintain the overall weight of the optical head assembly at a minimum.